Elimination of an opacified crystal lens through an ultrasonic emulsification and implantation of a lens into an eye that has undergone the elimination of the crystal lens are commonly carried out in cataract surgeries. Nowadays, using a soft intraocular lens made of a soft material, such as a silicon elastomer or a soft acrylic material, an optical part of the intraocular lens is folded by an intraocular lens insertion device, and the intraocular lens in this state is pushed by a plunger to push out the lens from a nozzle, and is inserted into an eye through an incision which is smaller than the diameter of the optical part.
Intraocular lens insertion devices can insert an intraocular lens into an eye through a tiny incision, thereby reducing the possibilities of a corneal astigmatism or an infection disease after a surgery. To further reduce the possibility of a corneal astigmatism or an infection disease after a surgery, it is desirable to minimize an incision for inserting an intraocular lens into an eye as much as possible.
In order to minimize an incision, however, it is necessary to fold an intraocular lens in a smaller size. Further, it is necessary to fold an intraocular lens in a predetermined shape in order to fix the intraocular lens at a predetermined position in the eye through the small incision.
For solving these problems, it is disclosed that a transition part in which a lens is folded during the movement of an intraocular lens therein has a basal end of an approximately rhombic shape that is gradually deformed into a circular shape at a leading end thereof (For example Patent Document 1).    Patent Document 1: Specification of U.S. Pat. No. 5,275,604